SSC-FPB Test Requirements

M. Arafin, Ph.D.Project Leader, Sour Grade Research & Development

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SSC - Four Point Bending (FPB) test

Acceptance Criterion• API 5L Annex H acceptance criterion: 72% SMYS

• NACE TM0177 has not adopted the test yet – in progress

• However, NACE MR0175 stipulates the acceptance requirements for such test (80% AYS)

• FPB, however, is less conservative than the Method A test or even the actual pipe test because only the outer surface of the specimen is in tension.

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FPB Results – 110ksi equivalent grade

SampleID

Rt0.5

(MPa)Rm

(MPa)

Test Stress(% of Rt0.5)

(%)

Failure (F)/No-Failure (NF)

0°-1

809 902

80 NF

0°-2 90 F

120°-1 80 NF

120°-2 90 F

240°-1 80 NF

240°-2 90 F

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110 ksi equivalent grade: SSC Method A

TestCell(#)

Rt0.5

(MPa)Rm

(MPa)

Test Stress(% of Rt0.5)

(%)

Time toFailure(h:m)

1

809 902

80 36:432 80 5:063 90 1:194 90 2:23

Extremely low failure times were observed!

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Threshold stress comparison

Ikeda et al. (1987) Kobayashi et al. (1987)

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Proposal

Confidential - ArcelorMittal Global Research and Development Gent 6

Specific Proposal

Request approval and funding for an API research study to determine the correct equivalence of applied test load/acceptance criterion for SSC-FPB with SSC Method A Methodology

Threshold stress for Method A will be determined first for a given material and process condition. The same material will then be tested using FPB with gradually increasing test loads to determine the failure stress. The same procedure will be repeated for a planned matrix of grades and process conditions in order to determine whether the threshold stress difference between the two test methods is nearly identical (e.g. always X-MPa higher in FPB) irrespective of test material or process conditions, such as the one reported by Ikeda et al. or can be expressed with other appropriate parameter. 

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Proposal contd.

Confidential - ArcelorMittal Global Research and Development Gent 7

The full range of API 5L grades must be considered for the study; however, higher strength grade such as X70MS will be examined first since the chance of failure is much higher compared to low strength grades like X42MS. Non-sour grades can also be used for this study since the objective of the tests is to determine the difference in threshold stress between the two test methods, and not the qualification of the materials. Anticipated outcome

Provide a guideline on the test load/acceptance criterion equivalence between Method A and FPB tests. It may be inserted as a NOTE in section H.7.3.2 as follows: “Applied test load/acceptance criterion for the FPB test should be X (appropriate equivalence parameter to be determined) higher than the agreed acceptance criterion of the Method A test”

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THANK YOU